This invention pertains to a battery powered medical implanted device, but more specifically, to a self-testing circuit for periodically and automatically testing the battery condition of such a device. Related subject matter can be found in commonly owned U.S. patent application Ser. No. 370,191, abandoned in favor of co-pending U.S. patent application Ser. No. 478,038 entitled Implantable Cardiac Defibrillator Employing Biopolar Sensing and Telemetry Means, incorporated herein.
The aforementioned U.S. patent application illustrates an example of one type of medical device in which this invention may be used. Because many implantable devices, if they are to perform electrical diagnostic and monitoring functions, are battery powered, after a period of time, the battery and/or the device must be surgically replaced, thus requiring the patient to submit to operative procedures. If the medical implant performs a critical life saving function, then it would obviously be of utmost importance to assure failsafe operation, not only of the circuit components which perform the monitoring and diagnostic functions, but also of the storage batteries.
Under current medical practice, battery operated devices are replaced after the passage of a predetermined time period or after performance of a certain number of treating events by the implant. In a standby defibrillator of the type described in above-mentioned U.S. co-pending patent application Ser. No. 478,038, the battery is replaced approximately every three to three and one-half years, or in the case of frequent issuance of high-energy defibrillating pulses, after issuance of about every ninety to one hundred defibrillating pulses. Sometimes, however, good batteries are unnecessarily replaced because their scheduled life, rather than their actual life, have passed, and this obviously presents an inconvenience to the patient. Such unnecessary replacement might result from favorable operating circumstance of the implanted medical device or from an extremely durable battery exceeding its manufacturing design specification. On the other hand, a battery might prematurely fail because it does not meet its intended design specifications, although being tested for such prior to release from its manufacturer. Other circumstances, as well, affect the actual life of the battery.
Thus, to minimize unnecessary surgical operations and/or to prevent premature battery failure, it is a general objective of the present invention to provide a battery condition warning system for use in a medical implanted device which warns the patient of an impending battery failure so that the patient may take remedial action.
Another objective of the present invention is to provide a battery condition warning system operative to test a battery both during the operation of the medical implanted device and at fixed periodic time instances during automatic self-testing cycles of the warning system.
A further objective of the present invention is to provide a battery condition warning system that enables the batteries to be replaced on an as-needed basis, rather than at fixed periodic time instances, thereby to minimize undue surgical replacement of the batteries and to reduce the likelihood of premature battery failure.